T-shirt design for Cthulhu and maybe his home in R'lyeh described as drowned wreckage of a city with its slimy green vaults with bizarre architecture, based on H.P. Lovecraft. Limited color palate please - mostly greens, blues, browns, blacks. Description is as follows: "A monster of vaguely anthropoid outline, but with an octopus-like head whose face was a mass of feelers, a scaly, rubbery-looking body, prodigious claws on hind and fore feet, and long, narrow wings behind."
Cthulhu has been described as a mix between a giant octopus, a man, and a dragon, hundreds of meters tall, with webbed human-looking arms and legs and a pair of rudimentary wings on its back
There is a great bit of detail on Google on the subject.
Here is another link with more descriptive details on the background possibility: http://bit.ly/2bbjrni